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Effects of Patterning and Spatial Confinement on Order in Self-Assembling Systems

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Supramolecular chemistry has proven to be an effective strategy for bottom-up fabrication of monodisperse, functional nanostructures. However, most applications require these nanostructures to be spatially or orientationally ordered. This thesis investigates patterning and spatial confinement as tools for controlling order in self-assembling systems. We first look to improve the ordering of polar, mushroom-shaped supramolecular aggregates through surface chemistry and addition of small molecule guests. Monolayer and bilayer films are 1 nm/layer thicker on hydrophilic oxide versus hydrophobic surfaces, suggesting more normal orientation and tighter packing of the molecules. By FTIR, 4-cyanobiphenyl incorporated into these films align normal to the surface with an order parameter f = 0.38. f of the host also increases from 0.2 to 0.7, possibly due to occupation of free volume and release of strain about the mushroom "stems" by the guest. We next develope methods for patterning and aligning 1D, supramolecular peptide-amphiphile (PA) nanofibers. Microcontact printing can directly pattern nanofiber arrays of submicrometer resolution. The features size increases with stamping time and glycerol concentration. Depending on the molecule, PA is deposited by direct contact or fluid transport through a water meniscus. By another method, sonication-assisted solution embossing, we achieve the simultaneous self-assembly, alignment and patterning of nanofibers over large areas. Alignment is due to steric confinement within submicrometer channels and a lyotropic liquid crystalline transition. Nanofibers can also be guided around turns by this technique. FTIR gives nanofiber orientation parameters of 0.2 to 0.4 and confirms that the nanostructures consist of axially aligned -sheets. Neural progenitor cells show preferential alignment of cell bodies parallel to these aligned nanofibers, hypothetically due to integrin clustering about the nanofibers leading to a restructuring of the cytoskeleton. Lastly, we examine the morphology of thin films of an oligothiophene amphiphile that assembles into 2D lamellae. Films thinner than the bulk d-spacing of 13.0 nm exhibit regular dotted and striped surface textures of 18 nm periodicity. These monolayer textures depend on the conformation, extended or amorphous, of the poly(ethylene glycol) segments that frustrate the packing of the hydrophobic segments. Friction-transferred TeflonĀ® substrates show promise for controlling the alignment of these textures.

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  • 06/27/2018
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